Thyroid patients at risk from ‘overdiagnoses’

Low-risk thyroid cancers that are unlikely to develop into anything sinister are being picked up by sophisticated scanning equipment, exposing patients to needless and harmful treatment, doctors have warned.

This includes unnecessary thyroidectomy, the surgical removal of all or part of the thyroid gland, according to doctors writing in the latest edition of the British Medical Journal.

Juan Brito, an instructor of medicine at the Mayo Clinic in Minnesota, argues that the expanding gap between the number of thyroid cancer cases diagnosed and the number of deaths from the disease suggests that low-risk cancers are being overdiagnosed and overtreated.

This may also be the case in Ireland where, according to National Cancer Registry data, incidence rates have increased significantly in both sexes since the mid-1990s, while mortality rates vary little from year to year.

About 40 females and 20 males per year were diagnosed with thyroid cancer during the mid-1990s, compared to 120 and 45 cases per year respectively during the late 2000s.

This “incongruity” between incidence rates and death rates is “most likely an effect of overdiagnosis”, said Dr Brito.

The upshot is that some patients are undergoing unnecessary treatments such as thyroidectomy, which can, in turn, lead to physical complications, financial and psychosocial burdens, and the need for lifelong thyroid replacement therapy.

Harry Comber, director of the Cork-based NCR, said the problem of overdiagnosis, due to more sophisticated imaging techniques, was not confined to thyroid cancer. He said it was a “general problem with a lot of cancers now”.

“Tumours are being picked up that wouldn’t normally be,” said Dr Comber. “We are seeing it in kidney cancer too. It seems likely that some of these would never have presented any risk or surfaced in a person’s life.”

However, the difficulty was that, once a tumour are found, it was “impossible to tell” if it would turn out to be dangerous and it had to be removed, said Dr Comber.

“It’s a difficulty and I don’t know if anyone has the answer,” he said.

The British Medical Journal article argues that zealous imaging, coupled with advanced diagnostic equipment, is fuelling an epidemic in diagnosis and treatment of thyroid cancers that are unlikely to ever progress to cause symptoms or death.

Dr Brito said the most compelling evidence that patients with low risk cancers are being overtreated is that, “despite a threefold increase in incidence of papillary thyroid cancer over the past 30 years, the death rate has remained stable”.

New technologies such as ultrasound, CT, and MRI scanning can detect thyroid nodules as small as 2mm. Dr Brito says observational evidence shows that small papillary thyroid cancers, which are a common autopsy finding, may never progress. Nonetheless, the detection of these cancers in patients without a family history of thyroid cancer or exposure to radiation “usually triggers intensive treatment”, said Dr Brito.

He and his colleagues have called for research be undertaken to identify the appropriate care for these patients. The doctors recommend avoiding thyroid cancer screening in the general population.